Restricted role of CRF1 receptor for the activity of brainstem catecholaminergic neurons in the negative state of morphine withdrawal

Rationale Evidence suggests that corticotropin-releasing factor (CRF) system is an important mediator in the negative symptoms of opioid withdrawal. Objectives We used genetically engineered mice lacking functional CRF receptor-1 (CRF1R) levels to study the role for CRF/CRF1R pathways in the negative affective states of opioid withdrawal. Methods Wild-type and CRF1R(-/-) offspring of CRF1R(+/-) breeders were identified by PCR analysis of tail DNA and were rendered dependent on morphine via intraperitoneal injection of increasing doses of morphine (10-60 mg/kg). Negative state associated with opioid withdrawal was examined by using conditioned place aversion (CPA), TH expression and TH phosphorylation were measured in different brain regions involved in addictive behaviours using immunohistochemistry. Results The weight loss in morphine withdrawn CRF1R(-/-) animals was significantly (p < 0.05) lower versus wild-type. The aversion for environmental cues paired with opioid withdrawal was lower (p < 0.001) in the CRF1R-deficient versus wild-type. Using dual immunolabeling for c-Fos, data show that naloxone-induced withdrawal increases the number of TH positive neurons phosphorylated at Ser40 or Ser31 that coexpress c-Fos in the nucleus of tractus solitarius (NTS)-A2 from wild-type and CRF-/- deficient mice. By contrast, the number of phospho-Ser40 or phospho-Ser31 positive neurons expressing c-Fos was lower in the ventrolateral medulla (VLM)-A1 in CRF-/--deficient mice. Conclusions Our study demonstrates an increased activity of brainstem catecholaminergic neurons after CPA induced by morphine withdrawal suggesting that CRF1R is implicated in the activation of A1 neurons and provides evidence that this receptor is involved in the body weight loss and in the negative aversive effects of morphine withdrawal.